Faculty Profiles - OKADA Akira

Papers - OKADA Akira

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Investigation of Effective Gas Shielding Method for a Wide-area in Vertical-position Laser Welding of Titanium Reviewed International journal

Yasuhiro Okamoto, Togo Shinonaga, Akira Okada

International Journal of Electrical Machining ( 29 ) 20 - 29 2024.3

Study on Surface Smoothing of Ceramics by Large-area Electron Beam Irradiation, Reviewed International journal

International Journal of Electrical Machining ( 29 ) 35 - 40 2024.3

Fundamental Study on Jetting Nozzle Diameter for Smooth Debris Exclusion in WIre EDM Reviewed International journal

Shixian Liu, Akira Okada

International Journal of Electrical Machining 29 27 - 34 2024.3

Application of large-area electron beam irradiation to micro-edge filleting Reviewed International journal

Togo Shinonaga, Hibiki Tajima, Yasuhiro Okamoto, Akira Okada

Journal of Manufacturing Processes 107 65 - 73 2023.12

Fundamental Study on Influence of Ground Surface Characteristics o n Mold Releasability in Compression Molding Using Thermosetting Phenol Resin Reviewed International journal

Qin Wang, Ryoji Kitada, Koki Yoshida, Akira Okada

Proceedings of The 10th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN 2023) 2023.11

Fundamental Study on CO2 Laser Forming of Carbon Fiber Reinforced Thermoplastic Sheet Reviewed International journal

Ryoji Kitada, Sena Kizaki, Yasuhiro Okamoto, Akira Okada

Proceedings of The 10th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN 2023) 2023.11

Fiber Laser Cutting of Steel Plate by Twin Spot Beam Setting in Scanning Direction Reviewed International journal

Yasuhiro Okamoto, Kota Morimoto, Naoki Kai, Akira Okada, Hiroaki Ishiguro, Ryohei Ito, Hiroshi Okawa

Journal of Laser Applications 35 ( 4 ) 042049:1 - 042049:111 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Laser Institute of America

This study investigated the effects of laser beam intensity distribution on the reduction of dross height in fiber laser cutting of a steel plate with 3.2 mm thickness. A twin-spot beam was produced by splitting a single Gaussian beam into two beams using a special axicon lens, and these beams were set in the scanning direction for cutting experiments. The power ratio of two beams (R:F = Rear power:Front power) was varied to discuss the intensity balance for the effective reduction of dross. After cutting experiments, ray tracing analysis was conducted using an optical analysis to calculate the absorbed power density distributions in the kerf. A smaller dross height of 18 μm can be achieved at a power ratio of R:F = 8:2, and its value is lower than that by a single Gaussian beam. At a power ratio of R:F = 8:2, the front beam of lower power is irradiated at the upper part of the workpiece, and the rear beam of higher power is absorbed at the lower part of the workpiece. Thus, effective heat input to the lower part of the workpiece can contribute to a reduction of the dross height. Variation of power ratio in the rear and the front beams is effective in controlling the cutting front shape, and the uniformity of absorbed power in the thickness direction can be improved by setting the rear beam of about four times higher power to the front beam of lower power to obtain a smaller dross height in the case of a 3.2 mm steel plate.

DOI： 10.2351/7.0001097

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Fundamental Study onHigh-quality Welding of Copper and Aluminum by Angled and Superposed Irradiation of Blue and Near-infrared Lasers Reviewed International journal

Yuki Yamada, Yasuhiro Okamoto, Akira Okada, Norio Nishi, Takeshi Yamamura, Katsutoshi Nagasaki, Kazunobu Mameno

Journal of Laser Applications 35 ( 4 ) 042005:1 - 042005-9 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Laser Institute of America

In order to achieve sustainable development goals, decarbonization and low-carbonization are required. Electric and hybrid vehicles are indispensable for the conservation of natural environment, and the lightweight construction and the effective transfer of electricity become important. Thus, copper and aluminum have been increasingly recognized as important materials because of their excellent materials’ properties. However, in the welding of these materials, it is difficult to obtain strong joints because there are problems in the brittle intermetallic compounds and the welding defects due to different melting points between copper and aluminum. Especially in the joining of copper and aluminum by copper side irradiation, aluminum-rich intermetallic compounds (IMCs) of brittle state result in the decrease of mechanical strength. Therefore, mild heat input from copper to aluminum would be necessary to reduce the brittle IMC. Angled irradiation might result in the mild energy input to aluminum because it can be expected that aluminum would be heated by the reflected light inside the keyhole generated in copper according to its high light reflection. In addition, stable welding can be expected by the superposed irradiation of blue and near-infrared lasers because of high light absorption rate of blue laser to copper. The angled and the superposed irradiation could achieve a stable welding state, and the generation of aluminum-rich IMC becomes smaller. Angled irradiation of a near-infrared laser showed equivalent joining strength to the superposed irradiation of two wavelengths, and the combination of angled and superposed irradiation achieved a remarkable increase of joining strength in a cross tensile test by 80%.

DOI： 10.2351/7.0001096

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Stabilizing the absorption of laser energy in welding of copper Reviewed International journal

Yasuhiro Okamoto, Norio Nishi, Togo Shinonaga, Akira Okada

15th International Conference on Materials Processing and Characterization (ICMPC) 2023.9

Investigation on improvement of wafer thickness uniformity in multi-wire EDM slicing Reviewed International journal

Takumi Yoshida, Haruya Kurihara, Yasuhiro Okamoto, Akira Okada

15th International Conference on Materials Processing and Characterization (ICMPC) 2023.9

Surface smoothing of additively manufactured Ti-6Al-4 V alloy by combination of grit blasting and large-area electron beam irradiation Reviewed International coauthorship International journal

Togo Shinonaga, Hiroya Kobayashi, Akira Okada, Toshiya Tsuji

The International Journal of Advanced Manufacturing Technology 127 5127 - 5137 2023.7

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Additively manufactured (AMed) titanium products are typically produced by electron beam melting (EBM), since oxidation of titanium alloy surface can be suppressed in vacuum environment. The surface roughness of AMed titanium products becomes more than 200 µm Rz, and the very rough surface would lead to reduction in fatigue strength. Therefore, a post surface finishing process is required. Abrasive blasting is one of the common surface smoothing processes of AMed metal products. Large surface roughness can be decreased, and compressive residual stress can be introduced to the surface. However, there is a limitation to reduction of surface roughness to several µm Rz. On the other hand, it was recently found that AMed metal surface produced by powder bed fusion with laser beam could be smoothed by large-area electron beam (LEB) irradiation. However, it is difficult to smooth surface with large initial surface roughness, and a tensile residual stress may be generated on the surface. In this study, surface smoothing and change in residual stress of AMed titanium alloy (Ti-6Al-4 V) were proposed by combination of grit blasting and LEB irradiation. Surface roughness of AMed Ti-6Al-4 V alloy significantly decreases from 265 to about 2.0 µm Rz by combination of grit blasting and LEB irradiation. Reduction rate of surface roughness by LEB irradiation linearly increases with decreasing mean width of blasted surface. Influence of the mean width on smoothing effect by LEB irradiation can be explained by thermo-fluid analysis. Moreover, tensile residual stress caused by LEB irradiation can be reduced when LEB is irradiated to blasted surface.

DOI： 10.1007/s00170-023-11857-5

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Other Link： https://link.springer.com/article/10.1007/s00170-023-11857-5/fulltext.html

Investigation on high-quality laser welding of copper and aluminum Invited Reviewed International journal

Yasuhiro Okamoto, Yuki Yamada, Akihiro Ochi, Akira Okada, Takeshi Yamamura, Katsutoshi Nagasaki, Kazunobu Mameno, Norio Nishi

International Conference on Processing & Manufacturing of Advanced Materials (THERMEC2023) 2023.7

Study on Joint Characteristics in Laser Butt Welding of AMed and Wrought Ti6Al4V Plates Reviewed International coauthorship International journal

Yasuhiro Okamoto, Togo Shinonaga, Yoshito Takemoto, Akira Okada, Akihiro Ochi, Ryuya Kishimoto, Sisa Pityana, Nana Arthur, Peter Omoniyi, Rasheedat Mahamood, Martin Maina, Esther Akinlabi

Welding in the World 67 ( 5 ) 1997 - 2005 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Titanium alloy Ti6Al4V has been widely applied to medical, automotive, and aerospace industries due to its excellent properties such as high strength and excellent corrosion resistance. On the other hand, additive manufacturing (AM) technology can give the freedom of design of the products. In order to spread the AMed products, the joining of AMed and wrought products are required, and it is important to understand the joint characteristics. In this study, butt welding of Ti6Al4V plate was conducted by fiber laser in argon shielding, and the joint characteristics of laser weld wrought/wrought, AMed/AMed, and AMed/wrought Ti6Al4V plates were experimentally investigated. The AMed plate has higher tensile strength than wrought plate but the elongation of AMed plate is smaller, since AMed plate has α’ martensite due to rapid cooling during laser irradiation in AM process. Then, the laser weld joint of AMed/AMed plates has higher tensile strength, but smaller elongation than that of wrought/wrought plates. The weld joint of AMed/wrought plates shows good welding state, since small heat input leads to formation of small weld bead with higher hardness between wrought and AMed plates.

DOI： 10.1007/s40194-023-01533-3

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Other Link： https://link.springer.com/article/10.1007/s40194-023-01533-3/fulltext.html

Micro-welding of Glass by Multiple Spot of Picosecond Pulsed Laser with Spatial Light Modulator Reviewed International journal

Ryo Takashima, Yasuhiro Okamoto, Akira Okada

Technical Digest of the 24th International Symposium on Laser Precision Microfabrication – LPM2023 R3-S15-3 2023.6

Optimization of Dielectric Oil Resistivity on Wire EDM Characteristics Reviewed International journal

Shixian Liu, Akira Okada, Tomohiko Kitamura

Proceeding of the 16th international conference of the european society for precision engineering and nanotechnology 23 2023.6

Investigation on Laser Welding of Copper and Aluminum by Irradiation from Copper-side Invited Reviewed International journal

Yasuhiro Okamoto, Yuki Yamada, Akihiro Ochi, Takeshi Yamamura, Katsutoshi Nagasaki, Kazunobu Mameno, Norio Nishi, Akira Okada

Proceedings of Laser in Manufacturing 2023 176 2023.6

Fundamental Study on High-quality Micro-shape Fabrication on Monocrystalline Diamond by Nanosecond Pulsed Laser International journal

Kaichi Kawata, Yasuhiro Okamoto, Akira Okada

Technical Digest of the 24th International Symposium on Laser Precision Microfabrication – LPM2023 R3-S11-2 2023.6

Effect of scanning speed on molten metal behaviour under angled irradiation with a continuous-wave laser Reviewed International journal

Tatsuhiko Sakai, Yasuhiro Okamoto, Nozomi Taura, Riku Saito, Akira Okada

Journal of Materials Processing Technology 313 117866 - 117866 2023.4

Fundamental Study on Electrode Performance of Diamond Composite for EDM Reviewed International journal

Shun-ichiro Tsuetani, Koki Yoshida, Akira Okada

International Journal of Electrical Machining ( 28 ) 26 - 31 2023.3

Improvement in Mechanical Properties of AMed Al-Si Alloy Surface by Large-area EB Irradiation Reviewed International journal

Togo Shinonaga, Hiroya Kobayashi, Atsuhi Yamaguchi, Akira Okada

International Journal of Electrical Machining ( 28 ) 20 - 25 2023.3

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